It is known that a “push-to-talk” service (briefly, PTT service) allows a group of users to communicate with each other through a common channel. Typically, each user has a terminal capable of transmitting and receiving voice signals along the common channel. Typically, each terminal is configured in a default state wherein it can only receive voice signals. Besides, each terminal typically has a talk button. When a user wishes to talk, he pushes the talk button of his terminal, so that its terminal sends a talk request to a server. The server may reply to the terminal either with a talk grant or with a talk deny. In the first case (reception of a talk grant), the user is allowed to send a voice signal to the other users through the common channel.
For instance, the OMA Push-To-Talk Over Cellular (POC) standard, version 1.0.1 dated 28 Nov. 2006, Chapter 5, describes a telecommunication system capable of providing the above PTT service to a group of users having respective mobile phones. The telecommunication system described by the OMA standard comprises an IP-based packet-switched telecommunication network and a mobile access network (in particular, a GSM network or a UMTS network) to which users are connected by means of their mobile phones. Further, the IP-based packet-switched telecommunication network supports an IP Multimedia Subsystem (briefly, IMS) cooperating with a POC server. The POC server is in charge of managing groups of users wishing to communicate through the POC service. For accessing the POC server, a mobile phone is provided with a POC client. The POC client is configured to interact with the POC server. In particular, the POC client is configured to transmit talk requests and talk release messages to the POC server, and to receive talk grants and talk deny messages from the POC server. Besides, the POC client is in charge of managing a user contact list stored at the mobile phone, i.e. displaying the contacts on the mobile phone display, modifying the contacts (i.e. adding or removing contacts) and updating the presence status of each contact according to status update messages received from the POC server.
Recently, the PTT service (and in particular, the POC service described by the above cited OMA standard) is used also for allowing a user to exchange contents such as discrete contents (e.g. audio files, text files, video files, pictures, etc.) or streaming contents (e.g. audio streaming, audio/video streaming, etc.) either with other users or with a service provider. The ensemble of the PTT service and these PTT-based content exchange services will be termed “push-to-x services” (or, briefly, PTX services) in the following description and in the claims.
In case of POC-based PTX services, a POC client is therefore also responsible for managing contents exchanged by the user, which are stored at the mobile phone.
Recently, telecommunication service providers feel the need to provide these PIX services not only to users provided with mobile phones, but also to users provided with terminals supporting packet-switched communications. Examples of these terminals, which will be termed “data terminals” in the following description and in the claims, are: personal computers, PDAs, set-top-boxes or phones supporting packet-switched calls, such as VoIP phones.
In the art, solutions are known allowing to extend the PTT service also to terminals other than mobile phones.
US 2006/0105792 discloses a method for providing a push-to-talk service between PTT enabled devices and non-PTT enabled devices. First, the non-PTT enabled device is registered at a PTT interworking agent. Then, signalling data is received at an interface in a first format. The signalling data includes an identifier corresponding to one or more destination phones. Next, the signalling data in the first format is converted to a second signalling protocol at the PTT interworking agent. The push-to-talk signalling information is sent to a push-to-talk server and a destination address is located for each of the one or more phones associated with the signalling data. The signalling data is then routed to the one or more phones.
Further, US 2007/0010272 discloses a gateway between a push-to-talk type network and a second telecommunications network. This gateway includes means for creating a first instance of a first push-to-talk client adapted to communicate with a second push-to-talk client via a first telecommunications network; means for setting up a call with a service provider on a second telecommunications network; and control means adapted to set up a first communications channel between the first instance of the first push-to-talk client and the communications means to set up a logical session between a second push-to-talk client and the service provider.
EP 1 655 977 discloses a method for operating a push-to-talk session between at least a first terminal and a second terminal by use of a push-to-talk server of a cellular radio communications system, wherein data of the push-to-talk session is transferred via the push-to-talk server from the first terminal to the second terminal and vice versa. According to EP 1 655 977, the push-to-talk server processes data of the push-to-talk session in at least a first data format, the cellular radio communications system receives data of the push-to-talk session from the second terminal in at least a second data format and an interworking unit converts data from the second data format into the first data format and vice versa.